1. Field of the Invention
The present invention relates to a pretreatment method for a substrate surface to form a high-quality thin film thereon by reducing the difference in lattice constant between the substrate and a deposited material, and a thin film forming method using said pretreatment method.
2. Description of the Background Art
Conventionally, respective lattice constants of a substrate and a thin film being deposited thereon are different from each other, and when a thin film is is deposited on the substrate, such a difference in the lattice constants cause the lattice sizes of the deposited thin film to be also different from that of a substrate in size, so that the thin film may be formed on the substrate mostly in form of a polycrystal growth instead of an epitaxial growth, thereby making it difficult to form a high-quality thin film. In particular, when utilizing a chemical vapor deposition (CVD) technique in which an organic metal compound is dissolved by heating the substrate, and then is deposited on the substrate, respective layers in the thin film are closely related to a lattice structure of the substrate. Here, the surface state of the substrate significantly affects the growth of a material being deposited thereon.
A thin film growth on a substrate is influenced by factors such as a nucleus formation, a growth rate of nucleus and a nucleus orientation of already grown nucleus. Here, the nucleus formation is influenced by an initial state of the target substrate, and the nucleus orientation is affected by the main orientation of the original substrate. Therefore, when a thin film is formed on the substrate surface, the initial state of the substrate is most influential on the thin film formation.